Triple-Responsive Block Copolymer Micelles with Synergistic pH and Temperature Response

Multifunctional, stimuli-responsive block copolymers have been prepared via the sequential atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the in-house synthesized 1′-(2-methacryloxyethyl)-3′,3′-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline) (SPMA) monomer. Two PDMAEMA-b-PSPMA diblock copolymers, containing 3 and 14 mol % SPMA, were synthesized. The amphiphilic nature of the PDMAEMA-b-PSPMA diblock copolymers led to the formation of well-defined spherical micelles, comprising a hydrophobic PSPMA core and a hydrophilic PDMAEMA shell, in water. The combination of the pH- and temperature-responsive character of PDMAEMA with the pH-, temperature-, and light-sensitive properties of the PSPMA block has resulted in a complex responsive behavior of the copolymer micelles in aqueous solution, when applying three different external stimuli (i.e., light irradiation, pH, and temperature). More importantly, the synergistic response of the block copolymer micelles when varying simultaneously the solution pH and temperature is reported for the first time. Such multisensitive self-assembled nanostructures pave the way for the on-demand controlled capture and release of actives under complex environmental cues.